Pens being used today are mostly made of plastics or metals. Plastics are not likely to be subject to corrosion and can pollute the environment when discarded. Although metal can be reclaimed, the cost is high, and pens made from metal are not competitive with respect to cost in the market. A current trend in manufacturing is to substitute an environmentally friendly material for plastics. Polylactic acid (PLA) is a high molecular synthetic material with excellent biocompatibility and biodegradability. Polylactic acid is made from starch extracted from plants such as, corn, wheat, cassava, and so on. After the starch is degraded in the presence of an enzyme to obtain glucose, the glucose is fermented in the presence of lactobacillus to produce lactic acid. Finally, high purity polylactic acid is obtained through chemosynthesis. After polylactic acid products are discarded, the products are completely degraded into carbon dioxide and water under the action of microorganisms, water, acid, and alkali within three months after being in the soil or water. Subsequently, through photosynthesis, the carbon dioxide and water become the raw materials for starch in plants, thus avoiding polluting the environment. Accordingly, polylactic acid is a biodegradable material which is completely naturally recycled within the environment.
However, as polylactic acid contains a great many ester linkages and is weakly hydrophilic, biocompatibility with other materials is low. In addition, polylactic acid is a linear polymer and the range of the molecular weights of the polymerization products is too wide. This reduces the strength of the polylactic acid and fails to meet strength requirements for many products. Polylactic acid is a brittle material, the temperature leading to thermal distortion is low (54° C. under load), the shock resistance is poor, and the degrading periods are difficult to control. Pens made of conventional polylactic acid materials crack easily during production and assembly. In addition, as polylactic acid crystallizes slowly during injection molding, production efficiency is very low. In its conventional form, polylactic acid is not applicable to batch production, and the pens made of polylactic acid fail to meet the requirements for transportation in containers and routine storage.
Accordingly, in order for polylactic acid to be useful in making biodegradable articles, such as pens, new polylactic acid materials must be developed that overcome these problems.